The objective of this study is to evaluate the effect of chemotherapy and oral antibiotics on gastrointestinal function in a population of patients with acute non-lymphocytic leukemia in remission. Eligible patients are those patients receiving the chemotherapy combination of thioguanine and cytosine arabinoside for maintenance chemotherapy and receiving a specific group of oral antibiotics. The following laboratory tests are performed as a baseline, repeated at the end of the chemotherapy course and again while on oral antibiotics: serum carotene, serum Vitamin A, serum folic acid, serum D-xylose (2 hr) and urine D-xylose (5 hr). Twenty patients have been entered on study. Eleven patients have completed both sets of follow-up tests. Eight patients failed to complete both sets of follow-up tests, mostly due to the need for hospitalization to receive systems antibiotics. One patient remains on study. Because of the high drop-out rate in the second phase of the study, the study will focus on the effect of chemotherapy on gastrointestinal function. All 20 patients had the tests repeated at the end of their chemotherapy course.